The present invention relates to ink compositions for use in pens, particularly ball-point pen inks.
While there are long-recognized advantages to using aqueous inks in ball point pens, the viscosity of these inks must be carefully adjusted in order to avoid flow problems, such as leakage around the ball. To adjust the viscosity, these inks have been thickened with natural gums, e.g., xanthan gum. Inks containing gums, however, often exhibit undesirable performance characteristics, such as blobbing and inadequate ink flow as the ink supply in the pen is depleted. Attempts have been made to overcome blobbing by using a very small ball, but pens having a small ball size tend to have a "scratchy feel" during use.
Aqueous inks also tend to lack smoothness, good writing consistency, and are prone to drying out at the ball tip when the pen is left uncapped.